This invention relates to a casting wheel for a continuous casting machine of the wheel and belt type, in which the casting wheel has a casting ring mechanically coupled to a drive flange of the casting wheel.
In a machine of this type in which the molten metal is continuously cast into the casting ring closed over a certain arc by the metal belt, and is extracted in the form of a continuous bar where the belt leaves the ring, the drive flange and casting ring are subjected to different thermal conditions and hence to different states of expansion.
In this respect, at any moment during casting, the temperature pattern along the ring periphery is given by a curve which descends in a manner proportional to the quantity of heat removed from the ring and metal, this curve having a maximum at the point in which the molten metal is cast into the ring and a minimum in the zone in which the ring is free from metal.
The behaviour of the temperature at any point as a function of time is given by a curve identical with that heretofore described when the ring is rotating. The expansion of any ring portion induced by such a temperature condition is thus periodic, with a period corresponding to one revolution of the wheel.
The temperature pattern along the periphery of the drive flange is however practically constant.
These different temperature conditions generate a different deformation in the flange and ring. Thus while the drive flange practically maintains its original constructional shape, i.e. circular, under working conditions as the expansion is practically identical for each sector of the flange, the casting ring would, if not constrained by the flange, assume a geometrical form considerably deviating from the circular form, and generated by a continuous variation in the radius of curvature, which would determine a non-symmetrical ovalisation of the casting ring.
However in practice the ring is constrained by the drive flange, because of which the ring is obliged to maintain a geometrical configuration equal to that of the drive flange to which it is rigidly coupled, and therefore preserves a shape essentially equal to its original shape. This gives rise to tractive and compressive stresses between the flange and ring and to internal stresses in the ring, which not only lead to rapid ageing of the ring because of the periodicity of these stresses, but also in some cases to fracture of the coupling members.
In particular, where the coupling is obtained by a slot and key, in practice the slot in the casting ring often breaks because of the difference in the circumferential expansion of the portion between one slot and the next in the casting ring and drive flange respectively.